This set of plasma data came from the ISIS 2 (International Satellites for Ionospheric Studies) ion-mass spectrometer experiment. Ion densities of various ion species are available for the lower range (1-8 atomic mass units, H+, D+, He+, N++, O++) and the upper range (8-64 atomic mass units, O++, N+, O+, 18+, N2+, NO+, O2+). Also included in the data set are spacecraft position data, geomagnetic field intensity, F107 flux (daily solar radio flux), Kp indices, and Dst indices.

This data set consists of ISIS 1 and 2 (International Satellites for Ionospheric Studies)ionograms that have been obtained through a data restoration project. The ISIS ionograms, consisting of a fixed-frequency and a swept-frequency part, were digitized from the original ISIS telemetry tapes. The digitized sounder data consisting of 8-bit receiver-amplitude values collected at a 40 kHz rate contain the time and the frequency associated with each sounder pulse. The frequency of each sounder pulse is determined from a 3rd degree interpolation between the times of the frequency markers as identified in the sounder video during the A/D operation. Included in this data set are the average-resolution ionograms (averages of each 4 successive 40 kHz 8-bit values) in CDF format.
Software to read and display the individual CDF files is available at
ftp://nssdcftp.gsfc.nasa.gov/spacecraft_data/isis/software/isis2
These CDF files were produced at NSSDC from the original PI-provided ionogram data. Other ionogram data sets available at NSSDC include the full resolution ionograms and average ionograms both in the PI-provided (OS2) binary format, ASCII header files with pass-specific information and the PCM data which contain header, time, AGC, frequency-marker information and telemetry-level data from all other ISIS instruments. The binary average ionograms and the ASCII header files are available online at
ftp://nssdcftp.gsfc.nasa.gov/spacecraft_data/isis/topside_sounder/
ISIS 1 and 2 data are available to the extent permitted by telemetry scheduling and the location of telemetry stations. A list of stations can be found at
http://nssdc.gsfc.nasa.gov/space/isis/isis-table1-new.html
and their location on a worldmap is shown in
http://nssdc.gsfc.nasa.gov/space/isis/isis_station_lar.GIF (

These ionograms were digitized from the original ISIS-2 7-track analog telemetry tapes using the facilities of the former Data Evaluation Laboratory at the NASA/GSFC. This data restoration project is headed by Dr. R.F. Benson (NASA/GSFC). Ionograms were digitized at the rate of 40,000 16-bit samples/sec. This sample rate is higher than the Nyquist frequency of 30 kHz. The sample frequency of 40 kHz provides a measurement every 25 microseconds corresponding to an apparent range (c*t/2) interval of 3.75 km. Ionograms with this sample rate are designated as "full" ionograms because they have the full 3.75 km apparent-range resolution. The ionograms used for most analysis, and those available from CDAWeb, were produced by averaging every four samples of the sounder-receiver video amplitude output to yield an average value every 100 microseconds corresponding to an apparent-range resolution of 15 km. These ionogram files are referred to as "average" files with standard resolution. Each ionogram consists of a fixed-frequency and and a swept-frequency portion. The time resolution between ionograms is typically 14 or 22 seconds depending on the frequency sweep range.

This data set from the ISIS 2 (International Satellites for Ionospheric Studies) Swept-Frequency Sounder consists of electron density profiles for the ionosphere above the F2 maximum (topside ionosphere). The data set was generated from the averaged ionogram binary data (SPIO-00318) recorded by the Topside Sounder. The data are obtained with the TOPIST program, which analyzes the data, automatically scales the ionogram traces and resonances, and inverts the traces into an electron density profile. The same program is available for use to hand-scale the data if desired. Output data items include spacecraft position, electron density profile, assessment of quality, resonance and cut-off frequencies, and both the O-trace and X-trace.

This data set, provided by the Communications Research Centre (CRC) in Ottawa, Canada, consists of electron density profiles for the ionosphere above the F2 maximum (topside ionosphere). The data are computed from digital values of frequency and virtual height, scaled from ionograms that are measured by the ISIS 2 (International Satellites for Ionospheric Studies) Swept-Frequency Sounder. The data are ordered chronologically. Telemetry stations are not identified, but satellite location, Greenwich mean time of observation, solar zenith angle at the satellite, dip latitude at the satellite, total electron content down to the lowest height of topside signal reflection (normally near 300 km), and other relevant information is noted with each profile. The format gives sequences of numbers for each point scaled from the ionogram. These sequences include electron density at the successive points, and the coefficients a2, b3, b4, b5, etc. from which geometric heights can be calculated, using formulas 40 and 41 in J. E. Jackson, "The reduction of topside ionograms to electron-density profiles," Proceedings of the IEEE., p. 960, June 1969. These formulas can also be used to calculate interpolated density-height values. A CRC interpolation program (available at NSSDC) can be used with this data set. (